(1) Field of the Invention
The present invention relates to a tractive force sensing system for tractor, and more particularly to such system provided with a hydraulic device for a tractor having a draft control function to actuate an oil pressure control valve through a draft cam by tractive load from lower links.
(2) Description of the Prior Art
In order to provide a better understanding of a conventional tractive force sensing system for tractor, the description hereinafter will discuss such conventional tractive force sensing system including the relevant members, with reference to FIGS. 7 and 8.
A conventional feedback interlocking link means 26 shown in FIGS. 7 and 8, comprises a first vertical feedback link 35 and two links (second and third feedback links 36 and 37) for changing the direction of the swing movement of the first feedback link 35 so as to correspondingly actuate a draft cam 23.
The first feedback link 35 is pivotally supported by a pivot shaft 43 disposed at the frontal intermediate portion thereof, and is adapted to receive the movement of a support 31 in the F1 direction, by a follower cam 39 projectingly disposed at the lower end of the link 35. Therefore, the upper end of the link 35 is correspondingly inclined backward. Such backward inclination of the first link 35 is reverse to the forward rotation of a draft cam 23. In this connection, it is required to dispose two links 36 and 37 for changing the transmission direction of operation. Such mechanical and incorporated system is proposed for ease of assembling and disassembling. However, since it is necessary to dispose a plurality of links 36 and 37 for changing the transmission direction of operation as mentioned earlier, the promotion of assembling and disassembling efficiency cannot be fully realized.
Furthermore, since there are a number of parts to be connected, precise draft control cannot be sufficiently performed. Moreover, there are still problems as to durability and replacement of parts.
The description of other component elements shown in FIGS. 7 and 8 is omitted, since the general construction of such conventional tractive force sensing system except for the main portions thereof, is substantially the same as the general construction of a tractive force sensing system in accordance with the present invention to be discussed later. Therefore, such other component elements and their operations will be fully understood merely by referring to the detailed description of an embodiment of the present invention.